The invention relates generally to the heating of liquids, and specifically to those devices wherein rotating elements are employed to generate heat in the liquid passing through them.
Of the various configurations that have been tried in the past, types employing rotors or other rotating members are known, one being the Perkins liquid heating apparatus disclosed in U.S. Pat. No. 4,424,797. Perkins employs a rotating cylindrical rotor inside a static housing and where fluid entering at one end of the housing navigates through the annular clearance existing between the rotor and the housing to exit the housing at the opposite end. The fluid is arranged to navigate this annular clearance between static and non-static fluid boundary guiding surfaces, and Perkins relies principally on the shearing effect in the liquid, causing it to heat up.
An example of a frictional method for producing heat for warming a fluid is the Newman apparatus disclosed in U.S. Pat. No. 5,392,737. Newman employs conical friction surfaces in order to generate heat, the generated heat passing into a fluid reservoir surrounding the internal elements of the device, and where the friction surfaces are engaged together by a spring and adjustment in the compression of the spring controls the amount of frictional rubbing that takes place.
Such prior attempts at producing heat have suffered for a variety of reasons, for instance, poor performance during operation, and the requirement of complicated and expensive components. Scale build-up is another cost factor should subsequent tear down and refurbishment be then needed. Similarly, because friction materials eventually wear out, they must from time-to-time be replaced.
A modern day successor to Perkins is shown in U.S. Pat. No. 5,188,090 to James Griggs. Like Perkins, the Griggs machine employs a rotating cylindrical rotor inside a static housing and where fluid entering at one end of the housing navigates past the annular clearance existing between the rotor and the housing to exit the housing at the opposite end. The device of Griggs has been demonstrated to be an effective apparatus for the heating of water and is unusual in that it employs a number of surface irregularities on the cylindrical surface of the rotor. Such surface irregularities on the rotor seem to produce an effect quite different than the forementioned fluid shearing of the Perkins machine, and which Griggs calls hydrodynamically induced cavitation. Also known as the phenomena of water hammer in pipes, the ability of being able to create harmless cavitation implosions inside a machine without causing the premature destruction of the machine is paramount. These surface irregularities in Griggs are in the form of deep drilled holes over the length of the cylindrical rotor, and as such, the machining of such deep holes is both time consuming to perform and expensive. The Griggs machine has been shown to work well and is currently known to be used in a number of applications.
An important consideration concerning machinery operating at relatively high temperatures is the protection of bearings and seals against deterioration caused by high temperatures and pressures in the fluid entering and exiting the machine. In the case of Griggs, separate detachable bearing/seal units are deployed, externally attached to the main housing surrounding the rotor in order to space the bearing and seal members well away from the clearance surrounding the rotor. The requirement for such detachable bearing/seal units may increase expense and complication and there therefore is a need for a new solution whereby the effects of high temperatures and pressures are less harmful to such bearings and seals.
Whereas Perkins relies on an impeller to ensure there is always a steady and continuous supply of fluid being drawn through his machine, no such impeller is included in the machine of Griggs. As a result, the Griggs machine is less flexible as it can only perform by relying on a sufficient pressure head of fluid at the input, ie. mains water pressure, or a sufficient head of pressure from above situated holding tank, in order for sufficient fluid is able to make the journey through the annular clearance between rotor and housing. In neither Griggs or Perkins is the fluid itself propelled through the clearance by the action of the rotor rotation.
There therefore is a need for a new solution for an improved mechanical fluid heater, and in-particular where the action of the spinning disc-shaped rotor enables the liquid to be propelled radially outwards from a more central intake in a generally spiral trajectory past a multitude of cavitation implosion zones before reaching the periphery of the rotor.
The present invention seeks to alleviate or overcome some or all of the above mentioned disadvantages of earlier machines, in a device that is relatively simple to implement, preferably with fewer component parts, and or requiring fewer machining operations. The rotating member according to the invention performs with higher efficiency over a wider operating band, relative to the Griggs or Perkins machines. For instance, as the mass of the disc-shaped rotating assembly is potentially far less than the mass of the cylindrically-shaped rotors, it can operate at higher rotational speeds. The greater the rotational speed of the rotor, especially towards the tip of the leading edge, the closer to the speed of sound for improved shock waves by the cavitation implosion zones to maximum power efficiency in performance. As well as by keeping complication to a minimum and avoiding expensive and time-consuming machining operations, there would be advantage if the occurrence of the cavitational effect on the liquid through water hammer could be generated in openings that are relatively short in length, preferably punched or otherwise machined in a disc-like shape comprising a plurality of openings in several rows over the radial width of the disc, where one or more discs could be compactly packaged in the housing for simple economy, and preferably avoiding the detachable bearing/seal units of Griggs.